Lets avoid some confusions here.
![AnDi.png](./download/file.php?id=1714&sid=2a60ba1fba072e65906bbe8bbae49e72)
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- Ash coloured line represents an analogue signal
- Red coloured line represents a digital signal
Refer this image for following two parts.
What is the deference between Analogue data & Digital data.??
Analogue data represented in a continuous form, as contrasted with digital data having discrete values.
Here the analogue data is the wave represented by ash colour whereas the digital data set is {0, 4, 5, 4, 3....}.
*Analogue signals cover a range & Digital signals discreet values.?? Is this statement correct?
Analogue signals are continuous in time and level. Digital signals are continuous in time but discrete in level.
In the past we had Fm tuners with a range value. ex- 88.0 to 108.0 range.we can rotate the tuner and stop the meter in any place we want...
But now we have digital display FM tuners.It contain values between 88.0 to 108.0 ex-we can see meter goes 88.0>88.2>88.3......108.0 we can;t stop the meter like any place like old ones.we can use only the given values.
Is old FM tuner Analogue & new one is Digital?is this correct...can we apply the Analogue & digital theory for this FM tuner..or is this a bullshit question?..
![Wink ;)](./images/smilies/icon_e_wink.gif)
First lets clarify the modulation techniques in radio transmission. Mainly we have Analogue and digital modulation.
Analogue modulation methods
![Amfm.gif](./download/file.php?id=1713&sid=2a60ba1fba072e65906bbe8bbae49e72)
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In analogue modulation, the modulation is applied continuously in response to the analogue information signal.
A low-frequency message signal (top) may be carried by an AM or FM radio wave.
Common analogue modulation techniques are:
- Amplitude modulation (AM) (here the amplitude of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal)
- Double-sideband modulation (DSB)
- Double-sideband modulation with unsuppressed carrier (DSB-WC) (used on the AM radio broadcasting band)
- Double-sideband suppressed-carrier transmission (DSB-SC)
- Double-sideband reduced carrier transmission (DSB-RC)
- Single-sideband modulation (SSB, or SSB-AM),
- SSB with carrier (SSB-WC)
- SSB suppressed carrier modulation (SSB-SC)
- Vestigial sideband modulation (VSB, or VSB-AM)
- Quadrature amplitude modulation (QAM)
- Angle modulation
- Frequency modulation (FM) (here the frequency of the carrier signal is varied in accordance to the instantaneous frequency of the modulating signal)
- Phase modulation (PM) (here the phase shift of the carrier signal is varied in accordance to the instantaneous phase shift of the modulating signal)
Digital modulation methods
In digital modulation, an analogue carrier signal is modulated by a digital bit stream. Digital modulation methods can be considered as digital-to-analogue conversion, and the corresponding demodulation or detection as analogue-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet).
A simple example: A telephone line is designed for transferring audible sounds, for example tones, and not digital bits (zeros and ones). Computers may however communicate over a telephone line by means of modems, which are representing the digital bits by tones, called symbols. If there are four alternative symbols (corresponding to a musical instrument that can generate four different tones, one at a time), the first symbol may represent the bit sequence 00, the second 01, the third 10 and the fourth 11. If the modem plays a melody consisting of 1000 tones per second, the symbol rate is 1000 symbols/second, or baud. Since each tone represents a message consisting of two digital bits in this example, the bit rate is twice the symbol rate, i.e. 2000 bits per second.
According to one definition of digital signal, the modulated signal is a digital signal, and according to another definition, the modulation is a form of digital-to-analogue conversion. Most textbooks would consider digital modulation schemes as a form of digital transmission, synonymous to data transmission; very few would consider it as analogue transmission.
Fundamental digital modulation methods
These are the most fundamental digital modulation techniques:
- In the case of PSK, a finite number of phases are used.
- In the case of FSK, a finite number of frequencies are used.
- In the case of ASK, a finite number of amplitudes are used.
- In the case of QAM, a finite number of at least two phases, and at least two amplitudes are used.
So, now you are clear both AM and FM are two techniques in analogue modulation.
So it is just the electronic metre that doesn't let you fine tune as with tuning condensers. However 0.05 variance is enough for FM band I think.